The present invention relates to a heating apparatus for controlling the welding parameter of temperature for a pre-weld heating operation, interpass operation, or a hydrogen bake-out operation. The invention contemplates a novel induction technology for performing the following operations.
As will be apparent to one skilled in the art, the term “pre-weld heating” refers to the operation of preheating a section of pipe to the desired temperature before performing a welding operation upon a section of pipe. For example, in a pre-weld heating operation using P91 crome-moly steel pipe, the pipe is heated to a temperature range between 400 500 degrees Fahrenheit. The term “P91” is used to describe a common type of pipe used in a high-pressure application for transporting oil, gas, or steam. P91 is comprised of a chromium-molybdenum alloy having the chemical composition of 9Cr-1Mo—V (P91).
The term “hydrogen bake-out” refers to a finishing operation on a weld whereby a welded section of pipe in-situ is held at a constant temperature in order to remove any hydrogen impurities from the weld in preparation for a cutting of welding operation. A hydrogen bake-out helps prevent the weld-joint from pre-mature fracturing of the weld-joint or pipe in-situ.
The term “interpass temperature” refers to the temperature of the pipe between welding passes. A “welding pass” is the path taken by a single welding operation. For example, a welding pass for a section of pipe is the circumferential path taken around a weld joint for the pipe.
Prior Art: Several types of flexible electric powered heaters are disclosed in the prior art. For example, unexpired Russian Patent Number 2,115,265 (hereinafter, the '265 patent) issued on Jul. 10, 1998 discloses an electric heater used for the thermal treatment of structures, pipes, steam, gas and petroleum lines in situ for stress relieving only. The '265 patent discloses the use of a detachable ceramic insulator for the electric heater. The ceramic insulators are connected by means of elements in the form of bushes and fixed by catches. Insulator elements are connected according to the dovetail principle.
Accordingly, the prior art also discloses the use of a combined heating and insulating means for heat treating an object. For example, in expired U.S. Pat. No. 3,393,297 (hereinafter, the '297 patent), a heating and insulating means is disclosed for heat treating an object. The '297 patent discloses a flexible resistance wire which is covered by a heat insulating pad for heat transfer to the object to be heat treated. Insulator elements are connected according to the hook-and-latch principle.
Specifically, expired U.S. Pat. No. 4,255,649 issued to Fisher on Mar. 10, 1981 discloses a flexible heating element for use with plastic polyurethane piping. The heating element is comprised of a plurality of ceramic components strung together on a heating wire to form a flexible structure. Accordingly, the applicant modifies the expired Fisher patent and provides a new use for the heating element. Namely, the applicant has modified Fisher to be made amendable to pre-heating metal piping to address the deficiencies in the prior art for existing heating solutions directed towards oilfield piping.
In accordance with the present invention, a heating apparatus is disclosed which is directed towards the pre-welding operation of performing a hydrogen bake-out. The process of performing a bake-out operation is distinguishable from the expired '265 patent which is directed towards a stress relieving operation. In a typical “bake-out” operation the metal piping is heated to a temperature of 600 degrees Celsius, whereas in a typical “stress-relieving” operation, the metal piping is heated to a temperature range between 1200-1400 degrees Celsius.
Accordingly, the apparatus of the present invention is not amendable to be used for performing a stress relieving operation since the heating element would typically degrade or melt under a voltage load required to produce a temperature of 1200-1400 degrees Celsius. Applicant respectively submits that the '265 patent although potentially amendable to produce the temperature of 600 degrees Celsius required for a typically bake-out operation, it inherently does not address many of the prior art disadvantages which will be described herein.
Deficiencies of the Prior Art: Unfortunately, many of the prior art inventions are difficult and cumbersome to apply, remove or relocate from the weld area, which typically may be held within a tightly confined area. Additionally, many of the prior art inventions require a power source requiring the use of heavy machinery to provide a suitable source of power. For example, a generator truck is typically required for voltage requirements exceeding 110 volts. Each truck uses heavy cabling to supply power from the generator mounted on the truck to the heating apparatus which is typically located in a remote location from the weld site. The heavy cabling may present a hazard at the work site since the use of heavy voltage cabling present a safety hazard.
What is required in the Art is a portable heating apparatus for heat treating a section of oilfield pipe which may be easily retrofitted to the site to be heat treated. The heat treating apparatus should be amenable to be easily added, removed, or re-located to a new weld site. Additionally, the heating apparatus should not require the use of a heavy cabling, and/or the requirement of a high-voltage truck for supplying power to the heating apparatus.
In accordance with one aspect of the present invention, it is desirable in the art to have a method and apparatus for controlling a welding parameter such as temperature in order to improve the quality of a weld by controlling the interpass temperature, pre-weld heating operation or hydrogen bake-out operation.
In accordance with another aspect of the present invention, it is desirable in the art to have a method and apparatus for controlling a welding parameter such as temperature wherein the heating device does not require the use of a high voltage truck, and heavy cabling associated with supplying power to the heating device.
In accordance with yet another aspect of the present invention, it is desirable in the art to have a method and apparatus for controlling a welding parameter such as temperature wherein the heating device is easily amendable to be added, removed or re-located during the aforementioned operations.